Electro-dynamic actuator



Sgpt. 4, 1962 .1. M1 TYRNER 3,052,097

ELECTED-DYNAMIC ACTUATOR Filed Dec. 31. 1959 2 Sheets-Sheet 1 INVENTOR. \w BY W M M ATTOR EYS Sept. 4, 1962 J. M; TYRNER" ELECTRO-DYNAMIC ACTUATOR 2 Sheets-Sheet 2 Filed Dec. 31. 1959 INVENTOR. m. M

AT TOANEY$ BY W United States Patent Filed Dec. 31, 1959, Ser. No. 863,261 9 Claims. (Cl. 66-52) This invention relates to actuators for producing movement of parts in response to energizing of the actuator by an electric current.

The ever increasing use of electronic controls and data reducing equipment calls for simple electric actuators, which should be more suitable to cooperate with electric apparatus than the presently employed pneumatic devices.

It is an object of this invention to provide an improved electric actuator which delivers a working fluid under pressure against a diaphragm or to a fluid motor chamber connected with the part to be moved. The invention is suitable, therefore, for direct mechanical connections or for use in apparatus designed for operation by fluid under pressure.

The invention utilizes, as a working fluid, a liquid which is a good conductor of electricity. The preferred fluid is mercury. This liquid is placed in a chamber having electric coils which generate a rotating magnetic field which induces currents in the liquid. The ooaction of the field and induced currents causes rotation of the liquid and this movement of the liquid produces a centrifugal force. It is this centrifugal force that causes a rise in the fluid pressure; and the extent of the pressure rise is controlled by changing the strength of the magnetic field to make corresponding changes in the centrifugal force.

The principle of utilizing coiacting fields and currents has been used to obtain a centrifugal pumping operation for electrically conductive liquids, such as alloys of sodium and potassium; but is not believed to have been used before this invention for developing pressure in an actuator.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views;

FIGURE 1 is a vertical sectional view through an actuator made in accordance with this invention;

FIGURE 2 is a sectional view, on a reduced scale, taken on the line 2--2 of FIGURE 1;

FIGURE 3 is a sectional view, corresponding to FIG- URE 1, but showing a modified form of the invention;

FIGURE 4 is a sectional View, on a reduced scale, taken on the line 44 of FIGURE 3;

FIGURE 5 is a block diagram for the actuator shown in FIGURE 1, with manual control and remote position indication; and

FIGURE 6 is a block diagram for the actuator with feedback control tied into a larger system.

The preferred embodiment of the invention is shown in FIGURE 1. The main parts are two concentric cores 1 and 2, with a mercury filled gap 3 between them. The mercury in the gap forms a thin walled cylinder with good electric conductivity. Coils 4 are provided, which, when energized, excite a rotary field. Since this field traverses the mercury cylinder radially, it induces current in it. The coaction of the current with the field causes the mercury cylinder to rotate. This effect is similar to the rotation of a squirrel cage rotor in the field of an induction motor. Centrifugal forces, set up by the rotation, drive the mercury through channels 5 and 6 into a plenum chamber 7. The pressure, which is built up in the plenum chamber deforms a diaphragm 8. Thus 3,052,997 Patented Sept. 4, 1962 the diaphragm may be used to operate or actuate a connected device.

Change of the current in coils 4 changes the pressure in the plenum chamber, because the rotational speed of the mercury depends on the strength of the rotary magnetic field. Response is fast since only the mass of a thin walled mercury cylinder has to be accelerated or retarded.

The mercury which is moved from the gap 3 into the chamber 7 is replaced from a center pool 9 through connecting channels 10 and 11. In the center of this pool is a resistor 12, which is partially short circuited by the mercury. The amount of resistance reduction depends on the mercury level and consequently on the amount transferred to the plenum chamber. Therefore the resistor may be used to provide a feedback signal on the mechanical motion of the diaphragm. The ratio of diaphragm area to the pool cross section provides amplification of the actual mechanical displacement.

structurally the two cores 1 and 2 are supported and spaced by end covers 13 and 14. A center tube 15 ties the two covers together. Inside of the center tube is the pool 9, which may be inspected and replenished by removing a cap 16. The diaphragm 8 is fastened to the outer core 2 by means of two rings 17 and 18. Cooling fins 19 on the core 2 improve the dissipation of heat developed in the coils and in the rotating mercury.

A yoke 21 is secured to the center of the diaphragm 8 by a screw 22 or other fastening means; and motion of the diaphragm 8 is transmitted, to a part to be actuated, through a link 32.

Variations in the mechanical configuration are feasible. For instance the exciting coils 4 can be placed on the outer core. However this results in a winding which is harder to manufacture without offering any advantage in performance.

Another variation of the device is a design with a mercury disc instead of a mercury cylinder. This configuration is shown in FIGURE 3. Since the rotating mercury disc is not as well cooled as the mercury cylinder in the preferred design, a circulating flow is provided, which replaces continuously the heated up content of the disc.

FIGURE 3 shows a modified form of the actuator in which a housing 40 has its lower end closed by a diaphragm 42 held in place by a rim 44. It will be understood that the diaphragm 42 may be similar to the diaphragm 8 shown in FIGURE 1 and it may be attached to the housing in the same way and provided with motion transmitting mechanism such as already described in FIGURE 1.

Within the housing 40 there is an upper core 46 attached to the top of the housing and a lower core 48 supported by a flange 50 which extends from a center post 52. The center post is hollow and has a passage 54 opening through its bottom end and extending upwardly to cross passages 56 which open into a supply chamber 58 located above the top of the housing 40.

Above the cross passages 56, the interior of the post 52 is threaded and there is a needle valve 60 screwed into these threads and extending downwardly to the cross passages 56. When the needle valve 60 is screwed down as far as it will go, the lower pointed end of this valve closes the passage 54 so that no liquid can flow into the cross passages 56. As the needle valve 69 is backed off by screwing in a direction to raise it, the communication between the vertical passage 54 and the cross passage 56 becomes progressively larger.

A cap 62 screws over the upper end of the post 52 above the top of the supply chamber 58. This cap contacts with the top of the supply chamber when screwed down to its full extent. The cap 62 is removed whenever it is necessary to adjust the needle valve 60.

'induces the rotation.

There are windings 66 on the upper and lower cores 46 and 48, respectively. These windings, when energized, set up a rotary electric field in the space between the confronting faces of cores 46 and 48. When the housing 40 is filled with conductive liquid, preferably mercury, the portion of the liquid between the confronting faces of the cores 46 and 48 forms a disc and this disc is caused to rotate around the axis of the post 52 as a result of the co-action of the magnetic fields set up around the cores 46 and 48 by the current in the windings 66 and by the induced current in the liquid between the faces of the cores 46 and 48.

This rotation of the liquid disc between the cores 46 and 48 produces centrifugal force which acts on the liquid and causes it to flow radially outward from between the faces of the cores 46 and 48. This movement of the liquid under centrifugal force is indicated by arrows in FIGURE 3; and the liquid which moves outwardly against the sides of the housing 40 is forced downwardly and exerts pressure against the diaphragm 42 causing displacement of the diaphragm in the same manner as described in connection with FIGURE 1.

Some of the liquid flows upwardly through the vertical passage 54 in the center post 52 and flows through the cross passage 56 into the supply chamber 58. The amount of liquid which can thus escape from the housing 40 will depend upon the setting of the needle valve 60. If the needle valve is closed, no liquid can pass upwardly through the passage 56, but as the needle 'valve is set in progressively wider open positions, more liquid can move upwardly through the passage 54 and this limits the pressure on the diaphragm for any given excitation of the cores 46 and 48.

There are other vertical passages 70 leading from the liquid supply chamber 58 downwardly through a partition of the actuator and opening into a space within the center portion of the actuator at the inner side of the liquid disc which is formed by the portion of the liquid located between the confronting faces of the cores 46 and 48. As liquid is forced outwardly by centrifugal force, new liquid from the supply chamber 58 flows downwardly through the passages 70 to replace the liquid which has moved outwardly.

The pressure output of the actuator depends on the speed of rotation of the mercury cylinder (or disc). This speed, and with it the pressure output, may be controlled by varying the intensity of the rotary field which The control does not affect the speed of the field which stays constant, but the inevitable friction between the moving mercury and its stationary boundaries slows down the fluid cylinder (or disc) and slows it down more if the motion inducing force is weak.

Control of a rotary field requires control of the excitation of all phases. For economical reasons a twophase field is preferred which requires amplification of the command signal into a two-phase excitation. A simpler method of control is the use of two counter rotating fields which exert torques in opposite directions. The resulting torque acting on the mercury, then is the difference of the two torques. If one of the fields is of constant intensity, control of the other results in a controlled acting torque. It can be shown that this kind of control can be achieved by using a two-phase winding with one phase on a constant and the other on controlled excitation. Therefore one phase is connected directly to the line and only the other one to the amplifier, which now converts the command signal into a single phase excitation.

FIGURE shows a wiring diagram for the actuator shown in FIGURE 1. The actuator is manually controlled from a station 80. The resistor 12 shown diagrammatically in FIGURE 5, is in series with a signal device 82 connected with a power line 84. This signal device may be constructed as an ammeter with a scale graduated to show displacement of the diaphragm of the actuator.

As the level of the liquid 9 rises, a larger portion of the resistor 12 is short circuited by the liquid and the flow of current through the signal device 82 is increased. Conversely, as the level of the liquid 9 drops lower with greater displacement of the diaphragm of the actuator, a smaller portion of the resistor 12 is short circuited and the amount of current flowing through the signal device 82 decreases. It will be understood that this change in current is a function of the displacement of the diaphragm and a measure of the motion of the actuator.

A feedback control system is shown in the block diagram FIGURE 6. Coils 4 and resistor 12 are connected to an amplifier 90, which also is connected to the powerline 84 and the command station 92. The latter provides a command voltage which the amplifier compares with the feedback signal from resistor 12. If a difference exists the amplifier changes the excitation of coils 4 accordingly, and in the proper course of action the displacement of the mercury 9 around resistor 12 is changed until the feedback signal voltage equals the command voltage. Thus to every command signal a diaphragm position is coordinated, regardless of the forces which the diaphragm encounters in this position. The amplifier and command stations are devices as employed in conventional servo mechanisms.

The preferred embodiment and one modification of the invention have been illustrated and described, but other changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

What is claimed is:

1. An actuator including a chamber for containing an electrically conductive liquid, coils adjacent to the chamber and in position to set up a rotary electro-magnetic field that traverses the liquid in the chamber and that produces currents in the liquid so that coaction of the rotary field with a field of the induced currents causes rotary movement of the liquid, the actuator having space therein filled with liquid that is a continuation of the mass of liquid moved by the rotary field and in position to be acted upon by the centrifugal force developed by the moving liquid, and in which the chamber is shaped so that the principal part of the liquid that is subjected to the induced currents is a mass of liquid having substantially the shape of a hollow cylinder with an inside diameter much greater than the radial thickness of the mass of liquid forming said hollow cylinder.

2. An actuator including a chamber for containing an electrically conductive liquid, coils adjacent to the chamber and in position to set up a rotary electro-magnetic field that traverses the liquid in the chamber and that produces currents in the liquid so that coaction of the rotary field with a field of the induced currents causes rotary movement of the liquid, the actuator having space therein filled with liquid that is a continuation of the mass of liquid moved by the rotary field and in position to be acted upon by the centrifugal force developed by the moving liquid, and in which the actuator has a supply pool in communication with the chamber from which make-up liquid flows to replace that which is moved outwardly by centrifugal force, and in which the pool is at a level from which the liquid can fiow by gravity to the chamber and there are automatic means in the pool responsive to the depth of liquid in the pool for controlling a circuit of the actuator.

3. An actuator including a chamber for containing an electrically conductive liquid, coils adjacent to the chamber and in position to set up a rotary electromagnetic field that traverses the liquid in the chamber and that produces currents in the liquid so that coaction of the rotary field with a field of the induced currents causes rotary movement of the liquid, the actuator having space therein filled with liquid that is a continuation of the mass of liquid moved by the rotary field and in position to be acted upon by the centrifugal force developed by the moving liquid, and in which the actuator includes space in which the level of the liquid varies with the displacement of liquid by the centrifugal force, and the actuator has means responsh e to changes in the liquid level for controlling a circuit of the actuator.

4. The actuator described in claim 5 and in which there is space in the actuator from which liquid is withdrawn by the action of the centrifugal force, and the means responsive to changes in the liquid level are in the space from which the liquid is withdrawn.

5. The actuator described in claim 4 and in which the means responsive to the changes in the liquid level include a resistance coil that extends into the liquid and that is short circuited by the liquid to the extent that the coil is submerged.

6. An actuator including an inner core having a cylindrical outer lace, an outer core having an inner cylindrical face confronting the outer face of the inner core and forming therewith a cylindrical chamber, windings on one of the cores in position to set up, when electrically energized, a magnetic flux about an axis transverse of the axis of the cylindrical face of the core having the windings thereon, a movable wall of the actuator closing a space of the actuator that communicates directly with the chamber between the cores and at a location toward which the liquid is displaced by centrifugal force when liquid is caused to rotate by a rotary field produced by electrical energization of the windings.

7. The actuator described in claim 6 and in which the movable wall is connected with motion transmitting means for operating an element that is to be moved by the ac tuator.

8. The actuator described in claim 7 and in which the movable wall is a diaphragm closing a second chamber of the actuator, and the second chamber extends all the way across the end of the actuator beyond ends of the cylindrical faces of the cores, there are passages opening throuhg the inner face of the outer core and through which the chamber between the cylindrical faces of the cores communicates with said second chamber.

9. An actuator comprising a housing enclosing a chamher for holding electrically conductive liquid, a movable wall of the housing which is displaced by pressure in the housing, two cores within the chamber and having confronting faces spaced from one another to provide a discshaped space between said faces, windings on the cores for producing, when electrically energized, a rotary field in the space between the confronting cores, a liquid supply chamber separated from the chamber which contains the cores by a partition, a passage leading from the portion of the core chamber in position to receive liquid which has been displaced from between the core faces by centrifugal force, another passage through which liquid from the supply chamber flows into the core chamber at a location inward from the disc-shaped space between the confronting taces of the cores, and a needle valve for controlling the rate of flow of liquid between the core chamher and the supply chamber.

References @ited in the file of this patent UNITED STATES PATENTS 2,658,452 Donelian Nov. 10, 1953 2,730,951 Donelian et a1. Jan. 17, 1956 2,934,960 Robinson May 3, 1960 2,948,1l8 Carlson et a1. Aug. 9, 1960 

